Arrangement for improving maneuverability of a stable platform



June 15, 1965 H. LERMAN 3,188,870

ARRANGEMENT FOR IMPROVING MANEUVERABILITY OF A STABLE PLATFORM Filed Sept. 15. 1961 a Sheets-Sheet 1 AXES OF VEHICLE PITCH ROLL YAW FIGURE Ib FIGURE Io I4 FIGURE 40 AXES OF VEHICLE ROLL AXES or VEHICLE ROLL FIGURE 4b PITCH YAW PITCH YAW HAROLD LERMAN FIGURE 3b 'INVENTOR.

ATTORNEYS H. LERMAN June 15, 1965 ARRANGEMENT FOR IMPROVING MANEUVERABILITY OF A STABLE PLATFORM 3 Sheets-Sheet 2 Filed Sept. 15, 1961 POWER SUPPLY PITCH AXIS OUTER ROLL AXIS FIGURE 6 OUTER ROLL AXIS TORQUER INNER R0 PICKOFF HAROLD LERMAN INVENTOR.

. S v: E N Wm WM w A flfi a w m A R R m HR P SYNCHRO June 15, 1965 H. LERMAN ARRANGEMENT FOR IMPROVING MANEUVERABILITY OF A STABLE PLATFORM Filed Sept. 15. 1961 3 Sheets-Sheet 3 PITCH SYNCHRO COSINE WINDING INNER ROLL AXIS OUTER ROLL AXIS FIGURE 5 HAROLD LERMAN INVENTOR.

ATTORNEYS" angle exceeds 90".

United States Patent 3,188,870 ARRANGEMENT FGR Ill EROVING MANEUVER- ABILITY OF A STABLE PLATFORM Harold Lerman, Paramus, N.J., assignor to General Precision Inc., Little Falls, N..l., a corporation of Delaware Filed Sept. 15, 1961, Ser. No. 138,496 3 Claims. (tCl. 74-5.2)

The present invention relates to a stable platform, and more particularly to an arrangement for improving the maneuver capability of a four gimbal stable platform.

A stable platform is a gyroscopic arrangement mounted on a vehicle having three dimensional motion, providing a stable reference on the vehicle independent of the vehicle motion. Thus, the stable platform may be used for the purpose of launching missiles, navigation of the vehicle, etc. A four gimbal stable platform has all attitude capability. There is no restriction in pitch maneuverability. To achieve this properly, the stable platform must move its outer roll gimbal 180 as the pitch Ideally, the time to flip 180 should be instantaneous, at the 90 point. In practice, the in ner roll axis has a limited degree of freedom. The change or reversal of the outer roll gimbal is gradual. Thus, for a short period of time, the platform is receiving improper attitude information. Although attempts may have been made to provide a stable platform in which the maximum pitch rate during a loop maneuver was not limited by the time to move the roll gimbal, none, as far as I am aware was entirely successful when carried out into actual practice.

Thus, the object of the present invention is to improve the pitch loop maneuver capability of a four gimbal stable platform.

Other objects and advantages of the invention will become apparent from the following description and the accompanying drawing in which:

FIGURE 1a is a schematic diagram of a four gimbal platform in the situation where there are zero degrees roll and pitch;

FIGURE 1b illustrates the position of the axes of the platform shown in FIGURE 1a;

FIGURE 2 shows the conventional prior art configuration for controlling the outer roll axis in schematic form;

FIGURE 3a is a schematic diagram of the platform of FIGURE 1a during a loop maneuver at a pitch angle of 90 with no roll;

FIGURE 3b illustrates the position of the axes of the platform shown in FIGURE 3a;

FIGURE 4a is a schematic diagram of the platform of FIGURE la during a loop maneuver after the roll gimbal has flipped 90 with no roll;

FIGURE 4b illustrates the position of the axes of the platform shown in FIGURE 4a;

FIGURE 5 is a schematic diagram of the invention contemplated herein; and,

FIGURE 6 is a partially perspective view of the components depicted in FIGURE 5.

To better understand the present invention it is first necessary to visualize the problems which are to be solved. As shown in FIGURES 1a and 1b, the components of the platform are the azimuth gimbal 11, inner roll gimbal 12, pitch gimbal 13 and outer roll gimbal 14. The outer roll gimbal 14 is controlled by the output of inner roll synchro 15 which feeds a torquer 16 on the outer roll gimbal 14. This torquer 16 acting as a part of a servo loop is capable of flipping the outer roll gimbal 180". At equilibrium, the outer roll gimbal 14 is positioned so that the inner roll gimbal 12 is perpendicular to the pitch gimbal 13 which is the condition required for zero output from the inner roll synchro 15. The inner roll gimbal 12 usually has limited freedom to decrease size and weight of the platform.

During a pitch loop maneuver going through pitch, the platform depends on a servo loop to flip the roll gimbal i.e., inner roll synchro 15 provides a signal through amplifier 17 to outer roll torquer 16. Assuming a pure pitch maneuver, without roll or azimuth inputs, at 90 pitch the roll gimbal should flip 180 instantaneously. Yet, there is obviously no signal to cause this motion. Practically, there is always some yaw motion in the vehicle. As shown in FIGURES 3a and 3b, the inner roll axis at 90 is coincident with the yaw axis of the vehicle. Thus, there is a signal to start the roll gimbal moving. If the vehicle were able to remain at 90 pitch, the roll gimbal would flip exactly 90 so that the pitch and inner roll axis is disposed to sense any additional motion in pitch. As the vehicle continues to pitch, this additional signal from the inner roll synchro forces the outer roll gimbal to move the additional 90. Thus, the outer roll gimbal 14 has moved a total of 180.

When the vehicle is at 90 pitch, outer roll torquer 16 receives a signal from the inner roll pick-off 15 to start its 180 reversal. During this motion, the inner roll axis is displaced B as a function of the roll gimbal displacement D and a pitch rate 0 as per the following equations:

B o't Sin Di 1 S] D 2 D n where B is the inner roll gimbal displacement and is a relatively small angle 1) is the outer roll gimbal displacement 0 is the pitch rate of the loop maneuver t is time after the vehicle reaches 90 pitch.

D and 9 are assumed constant and the roll gimbal instantaneously attains the velocity of D. The maximum value of B is -2 o 3 rnaz. 0

Bmaxmust be less than the limited freedom of the inner roll gimbal for the proper operation of the platform.

If the freedom of the inner roll axis is :15", and l is 300/second, then the pitch rate cannot exceed 15 (300/sec.) 104 In many cases, the maximum pitch rate may be lower since the actual roll gimbal movement must be started by a yaw disturbance at the 90 pitch point.

The foregoing method of outer roll gimbal reversal has several disadvantages. For a pure pitch maneuver, the prior art method depends upon a yaw distubance to initiate the outer roll gimbal reversal. Also, there is no attempt to anticipate the roll maneuver and no action occurs prior to the vehicle reaching the 90 pitch point. Also, the inner roll axis is in the position for maximum pitch coupling when the pitch angle (actually 90 minus the pitch angle) is large. The maximum pitch rate capability of the platform is limited by the parameters set by Equation 3.

In the foregoing prior art method of outer roll gimbal reversal, there is a possibility of the inner roll gimbal hitting its stop which would lose the inertial reference completely.

Generally speaking, the present invention contemplates controlling the outer roll gimbal by switching the control from the sine winding of the inner roll synchro to the cosine winding of the pitch synchro. The time for switch- 43.3/second i the vehiclejapproaclies'90" pitch-angle". Thesignal from the cosine windingqof the pitch isynchro will :cause the outer roll gimbalto move exactly 90 at equilibrium; At

this position the inner roll synchro senses pitchof the aircraft. As soon as the vehicle exceeds the 90 :pitch angle, theinner roll synchro regains control 'ofthe outer roll gimbal and ,drives the'outer roll gimbal the remaining 90 to the final equilibrium :position. If thevehicle does not complete the loop maneuver, the inner groll synchro again regains control and bringsthe, outer roll gimbal back to its original position. TheIinner roll syne chro itself determines when it shall regain control of the outer roll gimbal. 1 F

Thus, the present invention programs the flipping of the outer roll gimbal decreasing the possibility of -l1avin'g the "inner roll 'gimbal hit its stop thereby losing the inertial reference. Thisis accomplished without requiring a larger sizeouter gimbalftorquer. The degree offreedom of the.

inner roll fgi'mbal is not increased; Basicallyythe pitch rate capability of the platform is increased by anticipating themaneuver;

To accomplish the foregoing scheme, itis evident that the outer roll gimbal is to be flipped by90 prior to the vehicle reaching 90 pitch; Under these conditions, the equation for B is:

Bell) cos D 4.

emeitszo (5) The condition for Equation 5 occurs when D is somewhere around 49 so that for the same condition of D and B the maximum pitch rate capability is increased by the fraction 104/32 or by 3.25. Y i

The proposed method assumes that when there is an almost pure pitch maneuver as indicated by a small roll angle, it is necessary to switch control of the outer roll gimbal. I This method of outer roll gimbal reversal has several advantages. For a pure pitch maneuver, a positive signal is created to start the outerroll gimbal reversal. The loop maneuver is anticipated and the outer roll gimbal as positioned accordingly. The inner roll axis is in the position 'for maximum pitch'cqupling when the pitch angle (actually 90 minus the pitch angle) is small. .It moves away.

from maximum'pitch coupling as the pitch angle increases.

so as to close the switch at a roll angle range of between about 8 (352) 'to about 0; Inner roll axis, circuit 31 is normally open and is controlled by one pole 41 of a two pole relay switch 36. Thermal relay 37 prevents premature openingof relay, switch 36. The other pole'38 of this two pole relay'switch is the'control'meansjfor feed: ing information to outer roll torquer 27;

During normal flight, these relay switches are unemgized and the control loop is from the inner roll transducer sine winding to the "outer roll torquer 27 across pole 38 of relay switch 36, the'switch being set on inner roll contact 39. Upon the proper conditions, the pole 38 will switch to contact 40 *o'fthe cosine winding of pitch synchro These predetermined conditions areset by the foregoing cam switch arrangement. For pitehangles below 80?, double pole relay 36 remains unenergized.

The inner, roll synchro 25 controls the outer'roll torquer 27. If the roll angle is Within about 10 to about +10", o'uterrollaxis switch 33 close'sf As'th'e aircraft goes into a loop maneuver, pitch axis switch "34 closes at about 80 or -80. Relayswitch 36 is energized and pole 38 moves from inner roll synchro sine winding contact 39 to pitch synchro cosine ;winding;contact 40 and at the same time closes the switch of pole 41 in the inner roll axis circuit 31 and by-pass circuit 32. =Ther' m'al switch 37 will-prevent the premature opening of: relay s'witeh 36 throu'g'h normally closed contact 42. At this tirrie 'the inner roll axis senses the vehicle pitch angle and inner roll switch 35 "closes. This is in the range of between about -8 to 0. The pitch synchro 26forces' outer roll torquer 27 to hip the outer roll gimbal 24,190? As the pitch angl goes beyond '90", inner roll switch 35"o'pens. Control from pole 33 is released and'swi'tches back to inner roll synchro 39. This provides theasignalnece'ssary for the o'u'terroll torquer27 to turn the outer roll gimbalz i the additional 90. To safeguard against'the extremely unli'kely condition where'the aircraft starts, but does not completea loop maneuver, it is possible to include-a rate switch 43 in series with'the power su ply andcircu it's 30,31 and 52. This ratefswitch canbe so set that if thera't'e, of the maneuver is too slow for the'aircratt'to completetheloop, the rate switch will open leaving the control from the inner roll synchro '25 to outer 'rolltorquer 27. Rate switch 43 is manufactured by General'Precisiom'I'iic, the assigne'efof the present patient application as a standard component. 1 I i k 3 It is to be observed therefor tlriat' the present invention provides for an improvement in afstableplatform which among othercomponents includes inner roll, pitch'and And, the maximum pitch rate is increased by a factor of 3% over the method of loop reversal of the prior art;

In carrying the present invention into practice, thein- I strumentation depicted in FIGURES Sz and 6 is prefer-; ably used; There, are as heretofore azimuth gimbal 21, inner roll gimbal 22, pitch gimbali23 and outer roll gimbal; 24, inner roll synchro 25, a pitchsynchro 26 and an outer roll torque'r27 are also provided. I

As previously'explained, in theyprior art method,rthe inner roll synchro 'sine winding which in this caseijis synchro 25 provides the :signal to .the outer roll torquer, i.e., torquer 27 through amplifier 28. ,But in accordance with'the present invention, at an appropriate time, controliis to be switched from the sine winding of inner roll, synchro 25 to the cosinewinding of the pitch synchro 26. To accomplish this, there is provided from .a power outer roll gimbals 22, 23,2 1, inner roll and-pitch synch'romeans 25 and 26 including sine and cosine'winiling s'thelrein,- sensing the rllandp'itclra'r ig'lfeis, and an outer roll torquer 12 7 controlling the outerroll g'ir r'ibi'all H The im@ proveinent comprises "the combination of control means as to switch control from the sine winding of the inner-roll sync hr'o means to the cosine winding of the pitch synchro means; an gate means ss, 314; iliilihi'l, switching said controlfr-omjhe inner roll synchro means "to thepitch synchro means-when the roll axis angleis under somewhere within 1 10 and the pitch axis is about 8'0; or and, control release means 35, releasin'g-saideontrol meansback to said inner roll synchro means as the pitch angle goes beyond 1 To prevent premature switching of controls, time delay "means in the formfof :a thermal switch 37 isgassociatedwith the controline'ans 3'8, and thermal switch 4 2:is, associated with controlre lease means, 35.; To preventfincorrect. operation in the maneuver rate switch is provided.

.Although the present inventionhas been described in conjunctionwith fpretenregl einbodimentsgit is to be un fderstood that m'odificationsfand variations may be re.- sorted to wit-houtdepartingfrom the: spirit andifscope of the inventionas, thoseskiiled in the art will readily un- 'derstand. Such modifications and variations a r-econ event of an incomplete maneuver or' non contemplated sidered to be within the purview and scope of the invention and appended claims.

Furthermore, as use-d herein, the expression synchro means is used as a generic term to include such devices as synchros, resolvers, control transmitters and control transformers. This type of device is well known in the art to furnish the sine and cosine of the angular displacement between the gimbals of gyros and platforms.

1 claim:

1. In a stable platform having inner roll, pitch and outer roll gimbals, inner roll and pitch synchro means sensing the roll and pitch angles, including sine and cosine windings, and an outer roll to-rquer controlling the outer roll gimbal, coupled and responsive to a signal from said inner roll synchro means sine winding, the improvement therein comprising; an outer roll and pitch axis circuit including an outer roll axis cam switch, the

cam of which is so disposed that said switch closes at a roll angle of about 10 to about+10, a pitch axis double cam switch, the two cams of which each cover a narrow are disposed about 160 apart so as to close at a pitch angle of about +80 and about 80, 21 two pole relay switch, one switch of said two pole relay switch being in said coupling between said outer roll torquer and said inner roll synchro sine winding disposed so as to switch said coupling from said outer roll torquer to the pitch synch-ro cosine winding; and, an inner roll axis circuit including therein, an inner roll axis cam switch with a cam are disposed so as to close the inner roll axis circuit for a roll angle between about 8 and 0, the second switch of said two pole relay switch, and said relay of the two pole relay so that said relay acts to close said inner roll axis circuit when said coupling to said outer roll torquer is switched, the inner roll axis circuit then acting on said relay while said cam switch is closed in the range of between about 8 and 0 of roll angle.

2. A device as claimed in claim 1, including a thermal delay switch in said outer roll and pitch axis circuit acting on said two pole relay switch to prevent premature opening thereof.

3. A device as claimed in claim 1, including a thermal delay switch in parallel with said inner roll axis cam switch to prevent premature opening thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,469,782 5/49 Phair 74-5.2 2,862,364 8/57 Gievers 74-5.2 2,900,824 8/59 Barnes 745.34 2,909,929 10/59 Granqvist 745.2

BROUG I-ITON G. DURHAM, Primary Examiner.

ORIS L. RADER, Examiner. 

1. IN A STABLE PLATFORM HAVING INNER ROLL, PITCH AND OUTER ROLL GIMBALS, INNER ROLL AND PITCH SYNCHRO MEANS SENSING THE ROLL AND PITCH ANGLES, INCLUDING SINE AND COSINE WINDINGS, AND AN OUTER ROLL TORQUER CONTROLLING THE OUTER ROLL GIMBAL, COUPLED AND RESPONSIVE TO A SIGNAL FROM SAID INNER ROLL SYNCHRO MEANS SINE WINDING, THE IMPROVEMENT THEREIN COMPRISING; AN OUTER ROLL AND PITCH AXIS CIRCUIT INCLUDING AN OUTER ROLL AXIS CAM SWITCH, THE CAM OF WHICH IS SO DISPOSED THAT SAID SWITCH CLOSES AT A ROLL ANGLE OF ABOUT -10* TO ABOUT +10*, A PITCH AXIS DOUBLE CAM SWITCH, THE TWO CAMS OF WHICH EACH COVER A NARROW ARC DISPOSED ABOUT 160* APART SO AS TO CLOSE AT A PITCH ANGLE OF ABOUT +80* AND ABOUT -80*, A TWO POLE RELAY SWITCH, ONE SWITCH OF SAID TWO POLE RELAY SWITCH BEING IN SAID COUPLING BETWEEN SAID OUTER ROLL TORQUER AND SAID INNER ROLL SYNCHRO SINE WINDING DISPOSED SO AS TO SWITCH SAID COUPLING FROM SAID OUTER ROLL TORQUER TO THE PITCH SYNCHRO COSINE WINDING; AND, AN INNER ROLL AXIS CIRCUIT INCLUDING THEREIN, AN INNER ROLL AXIS CAM SWITCH WITH A CAM ARC DISPOSED SO AS TO CLOSE THE INNER ROLL AXIS CIRCUIT FOR A ROLL ANGLE BETWEEN ABOUT -8* AND 0*, THE SECOND SWITCH OF SAID TWO POLE RELAY SWITCH, AND SAID RELAY OF THE TWO POLE RELAY SO THAT SAID RELAY ACTS TO CLOSE SAID INNER ROLL AXIS CIRCUIT WHEN SAID COUPLING TO SAID OUTER ROLL TORQUE IS SWITCHED, THE INNER ROLL AXIS CIRCUIT THEN ACTING ON SAID RELAY WHILE SAID CAM SWITCH IS CLOSED IN THE RANGE OF BETWEEN ABOUT -8* AND 0* OF ROLL ANGLE. 